January/February 2019^ DISCOVER^51
SPACECRAFT FROM LEFT: ESA; NASA (4). ‘OUMUAMUA: ESO/M. KORNMESSER
Jupiter
The International Astronomical Union
announced 12 new moons in July, bringing
Jupiter’s total up to 79, more than any other
known planet. On one of those many moons,
the fiery Io, the Juno probe found a new
heat source, likely a volcano. Meanwhile on
frigid Europa, new analysis of old data from
the 1990s-era Galileo probe provided the first
good evidence for plumes of water vapor.Uranus
An April Nature Astronomy
paper informed us that
Uranus’ clouds are full
of hydrogen sulfide, the
same smell behind rotten
eggs and ... other gases.
And new supercomputer
simulations appearing in
July in The Astrophysical
Journal explained Uranus’
extreme cold and tilt (it
practically rotates sideways):
It’s the fault of a colossal
impact, early in the planet’s
life, with an object about
twice the size of Earth.Pluto
In the November issue of
the journal Icarus, scientists
analyzing data from the
2015 flyby of the New
Horizons probe created the
best maps yet of the former
planet and its largest moon,
Charon, revealing intricate
depressions, mountains
and plains. And according
to a June paper in Science,
dunes form on the
diminutive world the same
way as on Earth, albeit
with methane ice instead
of sand.Ultima Thule
New Horizons isn’t
through yet! More
than three years after
flying by Pluto, in the
waning hours of New
Year’s Eve 2018, the
probe will zoom past
an ancient frigid body
known as 2014 MU 69
and nicknamed
“Ultima Thule.” At
about a billion miles
past Pluto, it’ll be the
farthest planetary
encounter we’ve
ever had.‘Oumuamua
In 2017, astronomers found an
alien in our midst: the cigar-
shaped ‘Oumuamua, which
passed through our solar system
from parts unknown. It sped
away from the sun faster than
expected, so scientists argued in
Nature in June that it’s likely an
interstellar comet, since these
icy bodies often expel warming
gas and dust when they pass by
the sun, boosting speed.Saturn
The Cassini probe may be
gone, but it’s still giving.
In a Nature paper in
June, astronomers poring
through its data archives
of the moon Enceladus
announced they’d found
complex organic molecules
— a possible precursor
for life — lurking within
its ocean. And scientists
learned why so many of
Saturn’s moons have odd,
bulbous appearances:
A May paper in Nature
Astronomy suggests the
smaller bodies smash
together, forming the
weird shapes.